Sale 1:

Sold for Cloud 9 Toy Tailor (17)

No outpost

Seller: http://backpack.tf/profiles/76561198043075767#!/compare/1473811200/1473897600

Buyer: http://backpack.tf/profiles/76561198062639551#!/compare/1473811200/1473897600

X = 17

Sale 2:

Sold for 15 keys

http://www.tf2outpost.com/trade/28505965 - B/O of 15

Seller: http://backpack.tf/profiles/76561198140964928#!/compare/1475020800/1475107200

Buyer: http://backpack.tf/profiles/76561198066405673#!/compare/1475020800/1475107200

X = 15

Sale 3:

Sold for 14 keys + <0.5 keys in ref

http://www.tf2outpost.com/trade/28316191 - B/O of 15

Seller: http://backpack.tf/profiles/76561198014925037#!/compare/1472256000/1472428800

Buyer: http://backpack.tf/profiles/76561198048821113#!/compare/1472342400/1472428800

X = 14

Sale 4:

Sold for Steaming Samur-eye (12) + ~3 keys in items

http://www.tf2outpost.com/trade/28488655 - B/O of 14, was relisted afterwards

Seller: http://backpack.tf/profiles/76561198062639551#!/compare/1474243200/1474675200

Buyer: http://backpack.tf/profiles/76561198140964928#!/compare/1474588800/1474675200

X = 14 (capped by B/O)

Sellers:

17 keys:

http://www.tf2outpost.com/trade/28513624 - 1 month

http://backpack.tf/u/76561198066405673

Sales at:

17

15

14 (2x)

Going with 14-17